Propeller, propeller propulsion system and vessel comprising propulsion system

ABSTRACT

The invention refers to a propeller comprising a base ( 2, 15 ) and a plurality of blades ( 1, 14 ) extending from said base in an upstream tilted manner, i.e. in the direction corresponding to the forward motion direction (D 1 ) of the craft. The blades extend in a direction forming an acute angle α with the forward motion direction, 10°≦α≦80°. The invention also refers to a propulsion system including the propeller, as well as to a craft including the propulsion system.

FIELD OF THE INVENTION

The invention is related to propellers, such as naval propellers, aerialpropellers and fan propellers for turbojet engines.

BACKGROUND OF THE INVENTION

The propellers of conventional crafts comprise a base or “hub” fromwhich the blades of the propeller extend. The blades comprise a bladebody having two ends, namely, a “blade root” or “blade foot”, which iswhere the blade is joined to the base of the propeller, and an oppositeend called “blade tip”; the tip of the blade corresponds to the point ofseparation between a leading edge (or advancing edge) of the blade and atrailing edge (or following edge) of the blade; with regard to thepropeller, the terms leading and trailing refer to the movement of thefluid in which the propeller is operating.

A propeller is normally configured so as to rotate about an axis ofrotation, driven by a drive shaft joined to the engine of the craft andtransmitting motion from the engine to the propeller. The propeller isconfigured such that when rotating in a “normal” rotating direction, itpropels the craft in a first “forward” or “upstream” direction,corresponding to the forward motion direction of the craft, at the sametime it propels fluid in a second direction opposite to said firstdirection (herein, the term “direction” also includes the “orientation”of the direction); the second direction is also called the “downstream”direction. Both the first and second directions are substantiallyparallel to the axis of rotation of the propeller.

The blades normally have an elongated and curved cross section, and itcan be said that each blade body has two main surfaces, one concavesurface corresponding to the pressure side, and another convex surfacecorresponding to the suction side. For the blade to have goodperformance, the propeller must rotate in the direction of the bladepressure side, i.e. such that the pressure side “propels” the water.This rotational direction is the one corresponding to the “forward”motion of the craft; if the propeller is rotated in the oppositedirection, the craft “reverses” motion (with worse performance of thepropeller since it is the suction side and not the pressure side the one“propelling” the water: in reverse motion, when the propeller rotates inthe opposite direction, the pressure side, which is concave and acts asthe suction side, stalls since the boundary layer is released, causingturbulences, which worsens the performance).

In conventional or classic propellers, the blades are extended, in theirblade foot to blade tip extension, in a direction which is orthogonal orperpendicular (or almost perpendicular) to the axis of rotation of thepropeller. This is the configuration originally established so that theflow of water propelled by the propeller was displaced “downstream”, ina direction substantially parallel to the axis of rotation of thepropeller and substantially opposite to the forward motion direction ofthe craft. Hereunder, this type of propellers is called “classicpropellers”.

There are several variants of the aforementioned conventional or“classic” propeller configuration of. For example, in currently usedrecreational boats, the blades can have a certain “downstream”inclination, such that the blades extend, from the blade foot to bladetip, in a direction which, in a plane including the axis of rotation,forms an obtuse angle with the “first direction” mentioned above, i.e.with the direction corresponding to the forward motion direction of thecraft. Said obtuse angle can be between 95 degrees and 110 degrees,corresponding to a blade inclination of about 5-20 degrees “backwards”from the conventional position perpendicular to the axis of rotation ofthe propeller. This “inclination” can reach 30 degrees in some highperformance boats, and is known as rake or “backward rake”. The purposeof this “backward” or “downstream” rake is to reduce vibrations in thepropulsion mechanism (in the drive shaft, etc.).

On the other hand, marine propellers have been developed in which saidrake is not always obtuse, specifically, propellers are known in whichthe angle can be between 85 and 110 degrees (i.e. the blades of whichhave a rake of between 5 degrees upstream and 20 degrees downstream withregard to a plane perpendicular to the axis of rotation passing throughthe center of the hub), according to the operating conditions of eachengine and boat. It seems that the 5-degree upstream rake has beencarried out so as to increase the dynamic equilibrium of the freepropeller (when it is taken out of the water), under certain navigationconditions and turns. In the rest of marine propellers, in ships andsubmarines, the blades are usually perpendicular to the axis of rotationof the propeller, or slightly tilted “backwards” (=“downstream”) toreduce vibrations.

In aerial propellers, the blades are usually perpendicular to the axisof rotation of the propeller and in some cases, with the ends tilted ina direction contrary to the rotation to delay the occurrence of shockwaves.

In helicopter main rotors, the blades are mainly subjected to twoforces, an aerodynamic force parallel to the axis of the rotor,corresponding to the lift due to the blade, and another dynamic forcedue to the rotation, which is the centrifugal force. In an articulatedrotor, assuming the blade is rigid, the latter will take the equilibriumposition of the previous forces, forming a certain angle with the planeperpendicular to the axis of the rotor, called coning angle. This valueis normally less than 8 degrees, 4 degrees being the most frequentvalue. In some types of rotors, the assembly of the blade to the hub ofthe rotor is carried out with a theoretical coning angle of about 4degrees “upstream” for the purpose of reducing the bending moment at theblade foot.

Other variants of the conventional propellers mentioned above aredisclosed and illustrated in the following patent documents:

JP-A-58-126288 discloses and illustrates a naval propeller with anadjustment ring and with the main blades tilted “backwards”, i.e.downstream; the main blades have a small blade on the end thereof,tilted upstream, the main function of which is to increase the flowgenerated by the converging ring 15, increasing the thrust forceaccording to the document.

WO-A-91/07313 discloses a naval propeller with blades having two smallplates or fins on the ends thereof, one on each side, forming a 90degree angle with a plane perpendicular to the axis of rotation of thepropeller, for the purpose of decreasing the blade tip vortex.

U.S. Pat. No. 5,176,501 discloses a propeller composed of a square boxor diamond shape formed by blades, turned by (or which turns) a shaftpassing diagonally through the square box or diamond shape.

U.S. Pat. No. 1,438,012 discloses a propeller having two opposite,helical-shaped blades.

U.S. Pat. No. 283,592 discloses a naval propeller in which the mostperipheral part (the part closest to the tip) of each blade is tilted inthe rotational direction of the blades in order to reduce centrifugalaction.

U.S. Pat. No. 5,890,875 discloses a propeller with blades formed by thebending of a sheet, such that the sheet forms “loops”.

U.S. Pat. No. 4,664,593 discloses a fan with the peripheral end of theblades bent in the rotational direction of the fan in order to decreasenoise.

One drawback in relation, to conventional propellers, i.e. with classicpropellers, with the blades perpendicular to the axis of rotation of thepropeller or propellers with the blades slightly tilted “backwards”(=“downstream”) for the purpose of reducing vibrations, is thatconventional propellers have a relatively low performance due to thelosses caused by the blade tip vortex, crossflow at the trailing edge ofthe blades, and slip. This drawback seems to be particularly severe innaval propellers, where performance is many times 60%, which means thata large part of the power supplied by the engine is lost, at least inpart due to the discussed factors. The objective of the invention is toprovide a propeller and a propulsion system for crafts by means of apropeller with reduced losses due to blade tip vortex and crossflow atthe trailing edge, and with less slip.

DESCRIPTION OF THE INVENTION

A first aspect of the invention refers to a propeller comprising:

-   -   a base (many times also called the “hub” of the propeller);    -   a plurality of blades, each blade having a first end joined to        the base (this end is normally known as the blade root or foot)        and a second free end defining a blade tip separating a leading        edge (also known as “advancing edge”) of the blade from a        trailing edge (also known as “following edge”) of the blade;    -   the propeller being configured to rotate about an axis of        rotation, driven by a drive shaft of a craft, for the purpose of        propelling said craft in a first direction parallel to the axis        of rotation and corresponding to the forward motion direction of        the craft, propelling a fluid in a second general direction        opposite to said first direction;    -   the blades extending in a third direction from the first end        towards the blade tip (in most cases, said third direction        coincides with the direction in which the blade section extends        in the plane including the axis of rotation and blade tip).

According to the invention, said third direction forms, in a planeincluding the axis of rotation, an acute angle α with said firstdirection, 10°≦α≦80°.

In other words, the blades “are tilted forwards” or “upstream” (withregard to the axis of rotation), i.e. they are not perpendicular to theaxis of rotation or “tilted downstream”, as is the case with theconventional propellers discussed above. Thus, according to theinvention the tilted configuration of the blades forms a sweep surfaceor area of the propeller corresponding to a body which can besubstantially conical or frusto-conical and the diameter of whichdecreases in the second direction (“backwards” or “downstream”).

The expression “second general direction” refers to the “general”direction of the flow that “exits” the propeller. Said second directionis generally “backwards” or “downstream”, although logically there areturbulences, etc., making some “individual” portions of the fluid followother courses.

Preferably 20 ≦α≦70°, more preferably 30°α≦60°, even more preferably40°≦α≦50°. In a preferred embodiment, α=45°.

The propeller may have only two blades; for example, two-bladepropellers are frequently used in outboard engines and in airplanes.

However, the propeller can also have at least three blades; this type ofpropellers is many times preferable in displacement ships and the like.

The propeller preferably comprises at least three blades, preferablyequidistantly distributed around the base of the propeller.

The blades can have an elongated configuration in the direction from thefirst end (blade foot) to the second end (blade tip).

Each blade can have a leading edge, located upstream from a trailingedge, both the first edge and the rear edge substantially extending insaid third direction, substantially from the first end to the secondend. The blade tip separates the leading edge from the trailing edge.

A second aspect of the invention refers to a propulsion systemcomprising at least one propeller according to the invention and a driveshaft joined to the propeller such that the drive shaft can make thepropeller rotate about its axis of rotation. The shaft can rotate drivenby the craft engine incorporating the propulsion system.

The propulsion system can comprise a nozzle concentrically locatedaround the axis of rotation of the propeller and laterally envelopingthe propeller, said nozzle having a fluid entry front end and a fluidexit rear end. The use of the nozzle can be especially advantageous inmarine applications.

Each blade can be joined to the drive shaft, or to an element configuredas an axial extension of the drive shaft, by means of a retention braceor by means of a plurality of retention braces, which serve to preventthe blades from becoming deformed or displaced due to the forces actingon them during use thereof. Each retention brace is preferably arrangedperpendicularly (or substantially perpendicularly) with regard to theaxis of rotation of the propeller.

Each retention brace preferably has the shape of a blade in featherposition for craft cruising speed (the retention braces thus have notraction effect at cruising speed). When the braces have the bladeshape, they must have a symmetrical profile (with convex pressure sideand suction side) for minimum aerodynamic drag.

The propulsion system can be part of a turbojet fan, each blade beingjoined to a propeller base being part of the drive shaft constituted ofa rotor of the turbojet, each blade being joined to said rotor also bymeans of at least one brace. The propeller can be radially surrounded bya tube-fairing.

A third aspect of the invention refers to a craft including a propulsionsystem according to the invention. The drive shaft of the propulsionsystem is joined to the machine of the craft which transmits the turningmotion to the drive shaft. The craft can be an aquatic craft, asubmarine craft or an aircraft.

The least difficult option for the shape of the blades is that theentirety of the blades, from the root to the tips, i.e. along theirentire length, have a noticeably uniform upstream rake.

To explain with the greatest simplicity what takes place, that whichoccurs in a propeller with blades at a right angle, with α=45 degrees(i.e. the blades are tilted 45 degrees “forward” or “upstream”), will beanalyzed, operating in water at a considerable depth or in the air witha low number of revolutions per minute, with no other additionalelement, only the hub or base and the blades.

With this tilted arrangement of the blades, it has been verified that inany fluid, the fluid jet or jet stream generated by the propeller doesnot continue in diverging downstream directions (and orientations ofdirection) from the sweep area of the propeller, i.e. it does notcontinue in directions perpendicular to the conical sweep surface of thepropeller (however, these directions perpendicular to the conical sweepsurface are the actual thrust directions of the blades on the fluid). Inan “at first glance not logical” manner, both the fluid inlet flow inthe propeller and the fluid outlet flow follow a direction substantiallyparallel to the axis of rotation of the propeller (to not complicate theexplanation, it is stated herein that the direction is substantiallyparallel to the axis of rotation, although in reality the fluid jet hasa certain convergence in the downstream direction, as in the case of theclassic propeller). Thus, a deflection of the fluid occurs with regardto the “at first glance logical” directions that the fluid should followand which would be perpendicular to the conical sweep area (giving riseto a divergent jet displacing an enormous amount of fluid mass). Whatactually occurs is a physical phenomenon which can be called “staticfluid effect”or “external fluid effect” and having consequences similarin some (not all) aspects to the known “ground effect” in helicopterrotors, airplane wings or air-cushion vehicles, caused by the deflectionof the fluid on the ground. In the case of the present invention, thedeflection of the fluid occurs in the sweep area itself (and not on theground or the water, which are always at a certain distance from theblade sweep area). Effectively, the flow of the jet propelled by thepropeller is substantially parallel to the axis of the propeller, sincethis is where the entire fluid mass propelled by the propeller about itsaxis of rotation finds less drag for progressing in its movement.Therefore, it is the enormous drag provided by the fluid located in theperipheral directions perpendicular to the conical sweep area, theinertia or linear momentum thereof, which forces the flow which flowsout of the propeller to continue in the direction substantially parallelto the axis of rotation of the propeller. Therefore, there is adeflection of the jet or flow and, as it is known, when a jet undergoesdeflection by an external element, the larger the angle of deflection isand the closer the blades are to the area where the deflection occurs,the greater the increase of the reaction force of the nozzle, wing orrotor generating the jet. In the case of the invention, the deflectionis not caused by nearby ground or water, but rather by the fluid at restor in motion around the propeller, outside the limits of the slipstreamor the control volume, which behaves as a solid barrier. As is wellknown, when the deflection is caused externally by an element outside ofthe system in motion, a decrease of the induced angle of attack on theblades occurs, whereby decreasing the induced drag and increasing liftand, therefore, traction and performance of the propeller. This decreaseof the induced angle of attack generates fewer losses due to blade tipvortex and due to crossflow at the trailing edge. The pressure on thepressure side of the blades increases due to the deflection; thisphenomenon has an important additional positive contribution which is todecrease marginal losses at the blade tip and the crossflow at thetrailing edge. Although it is real, said deflection is difficult toobserve directly, since at first it seems that the flow, after “passingthrough” the blades, simply continues in the same direction it wasfollowing before reaching the propeller. However, said deflection, whichcorresponds to the “upstream” angle of inclination of the blades withregard to a plane perpendicular to the axis of rotation, can betheoretically understood. As is known, a change in direction isequivalent to an acceleration of the fluid, an acceleration which mustbe added to the apparent acceleration in the perpendicular direction,i.e. parallel to the axis of rotation. Therefore, the traction of thepropeller increases according to the sine of the upstream angle ofinclination of the blades, or the sine of the angle of deflection, whichhave the same value. This increase can be called “floatability”. If saidangle is 45 degrees, the “coefficient of floatability” would be 1.7 forthe equation which establishes the thrust or traction force, thereforeby this concept, traction increases by 70%—due to less slip—and apartfrom that, as previously explained, the induced drag decreases,therefore decreasing the torque absorbed by the propeller, thus furtherincreasing performance. It is necessary to take into account that for a15-degree angle of attack, the induced drag is approximately three timesthat of the parasite drag. It must also be taken into account that inthis case, unlike the ground effect, the deflection occurs in the bladesweep area, therefore the increase of thrust is maximum due to proximityof the deflection of the jet to the blades. Said “floatability” refersto a dynamic system, i.e. while it is operating in steady state, thepropeller and the fluid surrounding it interacting.

In the equation defining the thrust or traction of a classic propeller(force is equal to density times flow rate, and times jet exit velocityminus jet entry velocity: F=pQ(v_(ex)−v_(en))), in the propeller of thepresent invention, and to obtain said force, it would also be necessaryto multiply by one plus the sine of the upstream angle of inclination ofthe blades, therefore, for a 45 degree angle, it would be necessary tomultiply by 1.7, for a 30 degree angle, by 1.5, etc.; these figureswould correspond to the “coefficient of floatability”.

The invention therefore increases the power output (the aforementionedtraction multiplied by the speed of the craft).

On the other hand, the power consumed is equal to the power output plusthe kinetic energy that is lost in the unit of time in the slipstream(kinetic energy is equal to one half of the density times the flow rate,and times the square of the jet exit velocity minus the jet entryvelocity). The theoretical performance is the ratio of the power outputand the power consumed; although the power output increases due to lessslip, the performance is always less than one since there is alwayscertain kinetic energy lost in the slipstream. (Thus, the apparentparadox of a performance greater than one—which is impossible—is herebyresolved due to the extraordinary increase of thrust; the theory of themomentum used does not provide an exact explanation of the behavior ofthe propeller, but it can be understood that it serves as an approachand, especially, to generally explain why it works).

The increase of traction or thrust provided by the propeller of theinvention is maintained for any speed of the craft with regard to theclassic propeller (i.e. with regard to the propeller with the bladesperpendicular to the axis of rotation of the propeller).

In some naval applications with propellers very close to the surface, inorder to prevent excessive vibrations, the propeller can preferably behoused inside a nozzle concentric to said propeller and which envelopesthe propeller in the axial extension thereof, from the free ends orblade tips, upstream, up to twice its normal distance to the end of theroots or feet of said blades, downstream; this nozzle preferably has thefront part of the wall close to the free ends (tips) of the blades, i.e.its radial distance with regard to the blades is very small. Said nozzlecan be fixed, i.e. joined to the hull of the craft, or to theanti-ventilation plate or to the tail in the case of outboard engines.The indicated length for the nozzle can be the recommendable minimumlength.

In naval propellers, the component of the centrifugal force, which tendsto bend the blades, is offset by the reaction of the jet on the pressureside of the blades, since the density of the water is very high, and bythe structural resistance of the propeller (marine propellers areusually very heavy-duty).

However, in aerial propellers, the component of the centrifugal force isnot offset by either of these two factors due to the scarce density ofair (800 times less than the density of water). Therefore, it isappropriate (or necessary) to adopt additional measures, especially inview of the higher number of revolutions per minute, and taking intoaccount the lower structural resistance to bending (although it ispossible that there could be cases of aerial propellers having a smallnormal diameter and slight upstream rake in which, at low rotationspeeds, the additional reinforcement elements may be dispensed with).

In aerial applications such as a tractor propeller, each blade may bejoined, on the side of the suction side, to an extension of the driveshaft, by means of one or several retention braces (the drive shaft canpass through the hub of the propeller and be joined to it); saidextension of the drive shaft would be in upstream direction; thediameter of said extension of the drive shaft, as well as the material,can be the same as those of the drive shaft.

In aerial applications such as the pusher propeller, in which the engineis in front of or upstream from the propeller, each blade can be joined,on the side of the suction side, to the drive shaft by means of one orseveral retention braces. The drive shaft can be longer than what isusual for the classic propeller, giving way to a larger distance betweenthe engine and the propeller.

In the case of the tractor propeller, to obtain a higher performance andto decrease the aerodynamic drag of the retention braces, it isappropriate for each brace to have the shape of a blade in featherposition for cruising speed (i.e. the brace would have no tractorfunction, it would only serve to support the centrifugal force of theblades of the propeller).

To prevent or reduce vibrations caused by an excessive extension of thedrive shaft with regard to the base bearings, it is appropriate for theretention braces to be perpendicular to the extension of the driveshaft, whether they have the blade shape or not.

In fans for turbojets, each blade can be joined, on the side of thesuction side, to the rotor of the turbojet by means of one or severalbraces. Said rotor can constitute the drive shaft and can also servedirectly as a propeller base. The retention braces can be joined by theroot thereof to different disks of the rotor of the turbojet, and saidrotor can be provided with multiple sets of blades with theircorresponding braces along their length, the roots of the different setsof blades being fixed to respective disks of the rotor of the turbojet.Both the blades and braces can be surrounded by a fixed fairing tube.

In fans, it may be appropriate for each retention brace to have theshape of a blade in feather position for cruising speed. The retentionbraces are preferably fixed.

The blade roots and brace roots can be joined to the disks of the rotorof the turbojet by the locking pin system. According to the locking pinsystem, the roots are introduced in a housing or channel in theperiphery of a disk of the rotor and they are radially held by means ofa pin with axial retention.

The optimization conditions of this propeller are the following: thenormal diameter, geometric pitch, normal projection of the surface ofthe blades, i.e. the projection on a plane perpendicular to the axis ofrotation and the revolutions per minute, have the same quantitativevalue as in the corresponding classic propeller for the same engine, thesame reduction to the output shaft and performances of the craft with anincrease of drag corresponding to the increase of thrust (classicpropeller being understood as the one having the blades perpendicular tothe axis of rotation); the length of each blade is equal to the lengthof the conventional blade divided by sinα, and the surface of each bladeis equal to the surface of the classic blade divided by sinα, withregard to the corresponding conventional blade for the same engine, thesame reduction to the output shaft and the performances of the craftwith an increase of drag corresponding to the increase of thrust.

There is a correspondence between the concepts blade length and normaldiameter, as well as between perpendicular projection of the surface ofthe blades and the blade surface, but they do not mean the same.Although perpendicular projection, i.e. the projection of the surface ofthe blades on a plane perpendicular to the axis of rotation of thepropeller, is the same as in the case of assembling a classic propelleron the same engine, because of the upstream rake, its length is longerfor the same normal diameter and, therefore, its surface is alsogreater; although the normal diameter is the same, since the flowdirection is noticeably parallel to the axis of rotation of thepropeller, the solidity factor increases since the course of a fluidmolecule over the pressure side and suction side of the blades isgreater; for 45 degrees, the course increases approximately by 41%. Asis known, the solidity factor is the ratio between the surface of theblades and the sweep area.

In the technical literature, a blade is divided into a blade root orfoot, a body and a blade tip sometimes this last blade sector is calledblade end. The blade tip is the end point separating the leading edge(or “advancing edge”) from the trailing edge (or “following edge”) ofeach blade, according to the relative movement of the fluid over theblades.

If the blades are tilted downstream, the deflection of the jet will notoccur due to an agent outside of the system in movement air or watersurrounding it but rather because of the convergence of the jet itselfwith a speed increase, which would mean greater losses in the slipstreamdue to the increase of kinetic energy; the “floatability coefficient”would be less than one; in the case of the classic propeller, its valueis one.

The advantages of this invention are therefore a considerable increaseof the traction and the performance of the marine propeller, aerialpropeller or turbojet fan, for the same power used, i.e. consumed, withthe resulting reduction of the specific fuel consumption. In the takeoffrun of airplanes, for a 45 degree “upstream” rake of the blades, thereis 70% more thrust for the same power consumed, which is important sincethis is when the thrust is most needed. Concerning the headway in boatsor ships, the traction increase is less due to the head loss in thenozzle. (This is without taking into account the decrease of induceddrag, which increases the performance and indirectly the thrust in thepower output).

BRIEF DESCRIPTION OF THE DRAWINGS

A series of drawings will be very briefly described below which aid inbetter understanding the invention, and which are expressly related toseveral embodiments of said invention, presented as illustrative andnon-limiting examples thereof.

FIG. 1A shows a schematic side view of a propeller suitable, forexample, for submarines (the main function of which is to navigate whilesubmerged), with blades tilted at a 45-degree angle upstream with regardto a plane perpendicular to the axis of rotation.

FIG. 1B shows a schematic view analogous to the one in FIG. 1A, butshowing the section or cut of one of the blades on the plane includingthe axis of rotation and the blade tip.

FIG. 1C shows a schematic view of the propeller shown in FIG. 1A, butthis is a frontal view from downstream.

FIG. 2 shows a cross-sectional view of one of the blades of FIG. 1A.

FIG. 3 shows a schematic view of a two-blade propeller on which vectorsrepresenting the centrifugal force and pressure, as well as theircomponents, are illustrated.

FIG. 4 shows a schematic view of rectangular-plan blades operating intwo different positions, the first position (on the left) is like in theclassic propeller (perpendicular to the axis of rotation) and the secondposition (on the right) is tilted with a 45 degree angle upstream; thecourse of a fluid molecule over the surface of the blades is shown inboth positions.

FIG. 5 shows a schematic side view of a propeller with a nozzleassembled on an outboard engine.

FIG. 6 shows a schematic view of the structure shown in FIG. 5 but thisis a frontal view from downstream.

FIG. 7 shows a schematic side view of an aerial propeller with twoblades and a hub forming a single part, with its braces.

FIG. 8 shows a schematic view of the propeller with its slipstream andthe distribution of velocities in two sections at a certain distancefrom it; the angle of inclination of the blades and the angle ofdeflection of the flow passing through the propeller are indicated.

FIG. 9 shows a schematic side view of a fan for bypass turbojets,showing only two of the multiple blades with their correspondingretention braces.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIGS. 1A-C, 5, 7 and 9 show different propellers according to theinvention, comprising:

-   -   a base 2, 15 (in FIG. 9, said base forms an integral part of the        rotor 21 of a turbojet);    -   a plurality of elongated blades 1, 14, each blade having a first        end 1A, 14A joined to the base and a second free end defining a        blade tip 1B, 14B separating a leading edge (or “advancing        edge”) 1C, 14C of the blade from a trailing edge (or “following        edge”) 1D, 14D of the blade.

Each propeller is configured so as to rotate on an axis of rotation 100,driven by a drive shaft of a craft for the purpose of propelling saidcraft in a first direction D1 parallel to the axis of rotation 100 andcorresponding to the forward motion direction of the craft, propelling afluid in a second general direction D2 opposite to said first direction.The blades extend in a third direction D3 from the first end 1A, 14A tothe blade tip 1B, 14B. As shown schematically in FIG. 1B, said thirddirection corresponds to the direction in which the cut or section 1E ofthe blade extends in the plane including the axis of rotation 100 andthe blade tip 1B.

According to the invention, said third direction D3 forms, in a planeincluding the axis of rotation 100, an acute angle α with said firstdirection D1, 10°≦α≦80°. Specifically, in the Figures, α=45 degrees. Inother words, if compared to the “classic” blades perpendicular to theaxis of rotation, the blades are tilted “upstream” with an angle of(90°−α), in this case, with 45 degrees.

FIGS. 1A-1C show a propeller suitable, for example, for a submarine, theblades 1 of which are tilted 45 degrees upstream, as indicated byreference line 3 and the third direction D3 forming an angle α=45degrees with a first direction D1 corresponding to the forward motiondirection of the craft. The blades 1 are joined to a hub or base 2assembled on the drive shaft (not shown in FIGS. 1A-1C) by means of anattachment bolt 7; the upper blade in the Figure has the suction side 4and the lower blade has the pressure side 5; the support 6 of the baseof the propeller comes close to the center of gravity of the blades,therefore the dynamic equilibrium increases. The support bearing of theshaft of the propeller is inside the support 6, integrated in the hull 8of the craft, as seen in the figure. The bearing can be just radial orradial and axial if there is no other axial element inside. FIGS. 1A-1Conly show two opposite blades so as to not complicate the drawing.Normally, it is preferable for the propeller to have at least threeblades. In FIGS. 1A and 1B, arrows D4 and D2 indicate the direction ofthe jet or jet stream of water moving the propeller before and afterpassing through the propeller, respectively. In FIG. 1C, arrow 200indicates the rotational direction of the propeller.

FIG. 2 shows the concave-surface pressure side 5 and the convex-surfacesuction side 4; the figure is oriented in the plane according to FIG.1A, therefore the leading (or advancing) edge 1C of the blade 1 islocated in the upper left-hand part in FIG. 2, and the trailing (orfollowing) edge 1D of the blade 1 is located in the lower right-handpart.

FIG. 3 shows the vector representation of the centrifugal force F andits two components, one component perpendicular to the blade F2 whichgenerates the bending stresses and the other component is in the samedirection as the blade F1 generating stretching stresses, with the samemodulus, since the rake of the blades is 45-degrees. The representationof the pressure vector P of the propeller, its effective component P1and the other component P2 are also shown; the force P refers to thestatic pressure on the conical sweep area of the blades.

FIG. 4 shows the trajectory of a fluid molecule on the rectangular bladesurface, in the case of a non-tilted blade 1′ (i.e. a classic propellerblade according to that discussed above) (this case corresponds to thetrajectory from A to B), as in the case of a blade 1″ of a propelleraccording to the invention, tilted 45 degrees (this case corresponds tothe course from A1 to B1). As can be observed, the course (A1-B1) in thesecond case is exactly the diagonal of a square having as a side thecourse (A-B) of the molecule in the first case. Therefore, the solidityfactor increases.

FIGS. 5 and 6 show an outboard propeller with a cylindrical nozzle 9 andanti-ventilation plate 11; the cylindrical nozzle 9 is joined to theanti-ventilation plate 11 by means of bolts 12 passing through theanti-ventilation plate and housed in pegs 10 welded to the nozzle. Theanti-ventilation plate 11 is integrated in a tail 13 of an outboardengine. In FIG. 5, the arrows D2 indicate the direction of the waterthat has passed through the propeller and in FIG. 6, arrow 200 indicatesthe rotational direction of the propeller. (The other numericalreferences correspond to elements analogous to those already discussedin FIG. 1A).

FIG. 7 shows an aerial propeller with aerial blades 14 (with theirrespective leading edges 14C and trailing edges 14D), the blade in theupper part having the suction side 4 and the blade in the lower parthaving the pressure side 5; the hub or base 15 of the propeller, thedrive shaft 16, a connection flatbar 17 for connection of the shaft, anextension 18 of the drive shaft passing through the hub 15, retentionbraces 19 (which can be high traction-resistant solid steel cylinders),and bolts with nuts 20 coupling the hub or base 15 of the propeller tothe flatbar 17 of the drive shaft are also observed. The arrow 300 inthe drive shaft 16 indicates the rotational direction (corresponding toforward motion); the other four arrows D2 and D4 indicate the directionand orientation of the air jet passing through the propeller, before andafter passing through the propeller, respectively. The retention braces19 may have frusto-conical shaped “outer” ends, with a larger baselocated on the ends and a smaller base with the same diameter as thebraces, these frusto-conical ends being housed in respectivefrusto-conical housings made in the blades. Naturally, to decrease theaerodynamic drag of the frusto-conical ends, the latter can be machinedfor integrating their surface in the pressure side of the blades. Theretention braces can be joined to the extension 18 of the drive shaft bymeans of locking pins (not shown in the figure). If decreasing theaerodynamic drag and noise is desired, each brace can have a blade shapewith symmetrical profile, with the chord having the same value along theentire length of the brace and equal to the diameter of the smaller baseof the peripheral cone frustum, so that the brace can be insertedthrough the blade, and with said braces in the form of blades fixed infeather position for cruising speed, i.e. without tractor function.

FIG. 8 shows a schematic representation of the aerial blades 14 of theprevious figure, as well as the drive shaft 16; it also shows theupstream angle of inclination C (complementary to angle α) of the bladeswith regard to the plane perpendicular or normal to the drive shaft andpassing through the center of the hub or base of the propeller. Thefigure also shows the angle of deflection D between a line perpendicularto the blade and another line parallel to the axis of rotation of thepropeller, in one plane. It can be seen that the upstream angle ofinclination C of the blades as well as the angle of deflection D of thefluid are always equal (and complementary to angle α); in this specificcase, they are 45 degrees. The angle of deflection is formed by a lineparallel to the axis of rotation and by the direction the fluid jetwould follow as from the sweep area, if said “external fluid effect” didnot occur (i.e. following directions perpendicular to the conical sweeparea). However, in reality and according to that discussed above, thefluid is forced to an outflow substantially parallel to the axis ofrotation, in what is called “second direction D2”. “Deflection” as suchcannot be seen since the fluid follows the same direction before andafter the sweep area, but it does in fact exist. In reality, the angleof deflection D is not exactly the one shown in FIG. 8, but rather it issomewhat larger than the angle of inclination C of the blades sincethere is a certain convergence of the fluid, as can be seen in theboundary surface E of the slipstream. However, to simplify theexplanation and calculations, it can be considered that the angles C andD are approximately identical and that the direction of the fluid jetafter (downstream) the propeller is substantially parallel to the axisof rotation.

FIG. 9 shows the aerial blades 14 with the retention braces 19 thereofassembled on the rotor of the turbojet 21 (only two of the multipleblades that the mechanism has are shown for greater simplicity andclarity of the drawing). The fairing tube 22 surrounds the blades forthe purpose of reducing the speed of the air reaching the fan, as it isdivergent with regard to the direction of the current. The axialcompressor 23 is also schematically shown. It is appropriate for boththe roots of the blades 14 and the roots of the retention braces 19 tobe anchored to the disks of the rotor by the locking pin system, whichis one of the systems currently used for this type of mechanisms.

The retention braces 19 are especially suitable in aerial applications.However, propellers having a small normal diameter, low revolutions andup to a 15-degree rake (i.e. with α≧75°), it is likely that braces arenot necessary. Turbojet fans correspond to one particular application ofthe aerial propellers.

The materials, size, shape and arrangement of the elements will besusceptible to variation, on the condition that this implies noalteration of the basic concept of the invention.

Throughout the present description and claims, the word “comprises” andvariants thereof, such as “comprising”, do not aim to exclude othercomponents.

1. A propeller having a geometric pitch and the propeller beingconfigured so as to rotate about an axis of rotation when the propelleris driven by a drive shaft of a craft for the purpose of propelling thecraft in a first direction parallel to the axis of rotation andcorresponding to the forward motion direction of the craft, andpropelling a fluid in a second general direction opposite to the firstdirection; the propeller comprising: a base; a plurality of blades, eachblade having a surface defined by a first end joined to the base and asecond free end separating a leading edge of the blade from a trailingedge of the blade; the blade being oriented to have an angle of attack;the blade having a convex surface suction side extending in a thirddirection from the first end towards the blade tip, the third directionbeing a direction in which one section of the blade extending in a planeincluding the axis of rotation and the blade tip; the blade having theleading edge upstream from the trailing edge, the leading edge and thetrailing edge substantially extending in the direction from the firstend to the blade tip; the blade tip being an end point separating theleading edge from the trailing edge; the third direction forming anacute angle α with the first direction 10°≦α≦80°, in a plane includingthe axis of rotation; each blade having a length equal to a length ofone blade perpendicular to the axis of rotation divided by sin α andhaving a surface equal to a surface of one blade perpendicular to theaxis of rotation divided by sin α for increasing thrust provided by theblade.
 2. A propeller according to claim 1, wherein 20°≦α≦70°.
 3. Apropeller according to claim 1, wherein 30°≦α≦60°.
 4. A propelleraccording to claim 1, wherein 40°≦α≦50°.
 5. A propeller according toclaim 1, wherein α=45°.
 6. A propeller according to claim 1, wherein thepropeller has two blades.
 7. A propeller according to claim 1, whereinthe propeller comprises at least three blades.
 8. A propeller accordingto claim 1, wherein the blades have an elongated configuration in thedirection from the first end to the second end.
 9. A propulsion system,comprising at least one propeller according to claim 1, and a driveshaft joined to the propeller such that the drive shaft is operable toturn the propeller about the axis of rotation.
 10. A propulsion systemaccording to claim 9, further comprising a nozzle concentrically locatedaround the axis of rotation of the propeller and laterally envelopingthe propeller, the nozzle having a fluid entry front end and a fluidexit rear end.
 11. A propulsion system according to claim 9, whereineach blade is joined to the drive shaft or to an element configured asan axial extension of the drive shaft by at least one retention brace onthe suction side to withstand centrifugal force.
 12. A propulsion systemaccording to claim 11, wherein each blade is joined to the drive shaftor to an element configured as an axial extension of the drive shaft byat least two of the retention braces.
 13. A propulsion system accordingto claim 11, wherein each retention brace is arranged perpendicularly tothe axis of rotation of the propeller.
 14. A propulsion system accordingto claim 11, wherein each retention brace has a symmetrical profile anda shape of a blade in feather position for craft cruising speed.
 15. Apropulsion system according to claim 11, forming part of a turbojet fan,each blade being joined to a propeller base forming part of the driveshaft comprised of a rotor of the turbojet, each blade being joined tothe rotor also by at least two of the retention braces.
 16. A propulsionsystem according to claim 15, further comprising a fairing tube radiallysurrounding the propeller.
 17. A craft, including a propulsion systemaccording to claim
 9. 18. A craft according to claim 17, wherein thecraft is an aquatic craft.
 19. A craft according to claim 17, whereinthe craft is a submarine craft.
 20. A craft according to claim 17,wherein the craft is an aircraft.